A belt type continuously variable transmission transmits power using a belt wound between a drive pulley (primary pulley) and a driven pulley (secondary pulley).
When rapid deceleration occurs in a vehicle installed with a belt type continuously variable transmission such as that described above, a downshift is performed rapidly in accordance with the deceleration to secure a post-deceleration and post-stoppage restarting ability.
At this time, a gear ratio variation speed must be controlled to prevent belt slippage, but the gear ratio may not always be shifted to an appropriate gear ratio (a Lowest position, for example) as a result of this control during the rapid deceleration. When the vehicle comes to a halt in this situation, the vehicle cannot restart easily. In particular, when rapid deceleration occurs while traveling on an uphill road, the vehicle is more likely to come to a halt due to hill-climbing resistance, and therefore the vehicle stops before the downshift has been performed sufficiently. In this case, restarting is likely to be difficult.
To secure a restarting ability when a vehicle stops without having performed a downshift sufficiently, JP3-292452A discloses a gear ratio control device for a continuously variable transmission installed in a vehicle which, when a vehicle speed does not increase even though a throttle valve opening is large, performs a downshift by increasing the oil pressure of a secondary side (driven side) pulley and reducing the oil pressure of a primary side (drive side) pulley while a clutch is engaged, thereby causing a belt to slide longitudinally with the pulleys in a non-rotational state.